1. Field of the Invention
The present invention relates to a display device, and more particularly to a technique which is effectively applicable to a display device which arranges a printed circuit board connected to the display device by a flexible printed wiring board on a lower side of a display region.
2. Description of the Related Art
Recently, as a display device such as a display for a television receiver set or the personal computer (PC), a display device which is referred to as a “flat panel display” has been increased in number. As one example of the flat panel display, a liquid crystal display device which includes a liquid crystal display panel is named.
The liquid crystal display panel is a display panel which seals a liquid crystal material between a pair of substrates, wherein one substrate out of the pair of substrates includes a plurality of scanning signal lines, a plurality of video signal lines and a plurality of TFT elements which is arranged in a matrix array, for example.
The liquid crystal display device includes, besides the liquid crystal display panel, for example, a plurality of printed circuit boards which controls the generation of data signals of videos or images which are displayed on the display panel and controls timings of inputting the generated data signals to scanning signal lines and video signal lines. Further, when the liquid crystal display device is a transmissive or transflective liquid crystal display device, on a back side (back surface) of a display screen of the liquid crystal display panel, a light source referred to as a backlight unit is arranged. Further, the liquid crystal display panel, the printed circuit board, the backlight unit and the like are integrally assembled to each other using a frame member.
In the liquid crystal display device, the plurality of printed circuit boards is, for example, constituted of a printed circuit board (hereinafter, referred to as a Tcon substrate) which includes a timing controller, a printed circuit board (hereinafter, referred to as a drain PCB) which relays signals inputted into the video signal lines formed on the liquid crystal display panel from the Tcon substrate and the like. The Tcon substrate is generally mounted on the back surface of the frame member. Further, the drain PCB and the like other than the Tcon substrate are generally mounted on an outer peripheral surface side of the frame member, that is, on a surface of the frame member arranged substantially orthogonal to the display screen of the display panel in many cases. Here, for example, lines formed on the Tcon substrate and lines formed on the drain PCB are connected with each other by a flexible printed wiring board. Further, the lines formed on the drain PCB and the video signal lines formed on the liquid crystal display panel are connected with each other by way of a TCP or a COF which mounts a driver IC thereon, for example.
Further, with respect to the liquid crystal display device, for example, there also has been known a liquid crystal display device in which the drain PCB and the like other than the Tcon substrate are also mounted on the back surface of the frame member, the flexible printed wiring board is folded by substantially 180 degrees, for example, and lines formed on the drain PCB and the video signal lines formed on the liquid crystal display panel are connected with each other (for example, see the following patent document 1).
[Patent Document 1] JP-A-2003-195340
Here, conventionally, a liquid crystal display device which is used as a display for the television receiver set or the PC arranges the drain PCB on an upper-side side of the display region in many cases. However, along with the increase of a heat value of a driver IC and the increase of a heat value of a backlight attributed to a demand for high definition and a high speed operation (high response) of recent years, heat is accumulated in an upper side of a display region, that is, in an upper side of a housing and hence, the temperature of the liquid crystal display device is liable to be elevated. Accordingly, due to the influence of the heat accumulated in the upper side of the housing, operations of circuits formed on the Tcon substrates and the drain PCB leading to the deterioration of display quality.
Accordingly, in a recent liquid crystal display device, there exists a case that the drain PCB is arranged on a lower side of the display region.
However, when the drain PCB is arranged on the lower side of the display region, for example, there exists a drawback that short-circuiting is liable to easily occur in a connection portion between the drain PCB and the flexible wiring board. One of the reasons which give rise to such drawbacks is briefly explained in conjunction with FIG. 5. FIG. 5 is a schematic cross-sectional view for explaining one of the drawbacks of the conventional liquid crystal display device.
In the conventional liquid crystal display device which arranges the drain PCB on the lower side of the display region. FIG. 5 shows the cross-sectional constitution of a lower side portion of the display region in a state that the liquid crystal display device is arranged on a base, for example. In the example shown in FIG. 5, a backlight unit 2 which is constituted of a tubular light source 201 (fluorescent lamp), a reflector 202, a light diffusion plate 203, a lower frame 204 and the like is arranged on a back surface of a liquid crystal display panel 1. Further, the liquid crystal display panel 1 and the backlight 2 are integrally assembled with a lower frame 204, a picture-frame-like mold frame 8 which is arranged between the liquid crystal display panel 1 and the backlight unit 2, and an upper frame 9 which is arranged on a display screen 1a side of the liquid crystal display panel 1.
Further, a Tcon substrate 5 is mounted on a bottom surface 204b of the lower frame 204, and a drain PCB 4 is mounted on an outer peripheral surface 204a of the lower frame 204, that is, on a surface of the lower frame 204 which is arranged substantially orthogonal to the display screen 1a of the liquid crystal display panel 1.
Here, lines formed on the liquid crystal display panel 1 and the lines formed on the drain PCB4 are connected with each other by way of a semiconductor package 3A such as a TCP or a COF on which a driver IC is mounted, for example. The lines formed on the liquid crystal display panel 1 and lines formed on the semiconductor package 3A are connected with each other using an adhesive material such as a solder or an anisotropic conductive resin, for example. Further, the lines formed on the drain PCB4 and the lines formed on the semiconductor package 3A are mechanically connected with each other using a connector 401 mounted on the drain PCB4, for example. Here, the connection between the lines formed on the drain PCB4 and the lines formed on the semiconductor package 3A is not limited to the above-mentioned connection performed using the connector 401, and there may be a case that the lines formed on the drain PCB4 and the lines formed on the semiconductor package 3A are connected with each other using an adhesive material such as a solder or an anisotropic conductive resin.
Here, the lines formed on the drain PCB4 and lines formed on the Tcon substrate 5 are connected with each other by way of a flexible printed wiring board 7. The lines formed on the drain PCB4 and lines formed on the flexible printed wiring board 7 are mechanically connected with each other using a connector 402 mounted on the drain PCB4. In the same manner as the above-mentioned connection, the lines formed on the Tcon substrate 5 and the lines formed on the flexible printed wiring board 7 are mechanically connected with each other using a connector 501 mounted on the Tcon substrate 5, for example.
To briefly explain assembling steps of such a liquid crystal display device, first of all, an assembling operation of the backlight unit is performed such that the reflector 202, the tubular light source 201 and the like are housed in the lower frame 204, and the lower fame 204 is covered with the light diffusion plate 203. Next, the mold frame 8 and the liquid crystal display panel 1 are mounted on the light diffusion plate 203 of the backlight unit. Here, for example, on the liquid crystal display panel 1, the semiconductor package 3A, the drain PCB4 and the flexible printed wiring board 7 are already mounted, the liquid crystal display panel 1 is mounted on the mold frame 8 and, thereafter, the drain PCB4 is mounted on an outer peripheral surface 204a of the lower frame 204 by bending the semiconductor package 3A. Next, the upper frame 9 is arranged to cover the liquid crystal display panel 1, and the upper frame 9 and the mold frame 8, the upper frame 9 and the lower frame 204 are fixed to each other using bolts or the like.
Then, for example, the Tcon substrate 5 is mounted on a bottom surface 204b of the lower frame 204 using bolts, and the flexible printed wiring board 7 which is connected to the drain PCB4 is connected to the Tcon substrate 5.
In assembling such a liquid crystal display device in accordance with such steps, for example, in mounting the Tcon substrate 5 on the lower frame 204 using bolts, there exists a possibility that a metal foreign material 13 is generated between the Tcon substrate 5 and the bottom surface 204b of the lower frame 204. This operation is performed in a state that the liquid crystal display device 1 is rotated in the counterclockwise direction by 90° from a state shown in FIG. 5, that is, in a state that the bottom surface 204b of the lower frame 204 is directed in the upward direction and hence, the generated metal foreign material 13 stays between the Tcon substrate 5 and the lower frame 204. Accordingly, when the Tcon substrate 5 and the flexible printed wiring board 7 are connected with each other, for example, when the Tcon substrate 5 and the flexible printed wiring board 7 are brought into a state shown in FIG. 5, for example, without being aware of the presence of the generated metal foreign material 13, the metal foreign material 13 which stays between the Tcon substrate 5 and the lower frame 204 falls. Here, when the metal foreign material 13 falls along the flexible printed wiring board 7, the fallen metal foreign material 13 arrives at a connection portion between the connector 402 of the drain PCB4 and the flexible printed wiring board 7. Further, when the metal foreign material 13 intrudes into the inside of the connector 402, short-circuiting is liable to easily occur in the inside of the connector 402.
When the short circuiting is generated attributed to such a metal foreign material 13, for example, a circuit of the drain PCB4 performs an abnormal operation and hence, an abnormal lighting defect occurs in a lighting inspection of the liquid crystal display device which is conducted after assembling the liquid crystal display device. When the abnormal lighting defect occurs, the liquid crystal display device is disassembled once to find out causes of the abnormal lighting defect. After repairing the causes or exchanging the printed circuit board, the flexible printed wiring board or the like, the liquid crystal display device is assembled again, and the lighting inspection is performed. Accordingly, when the abnormal lighting defect fluently occurs in the inside of the connector attributed to the short-circuiting, there also arises a drawback that the efficiency of the assembling operation of the liquid crystal display device is lowered.
Here, the above-mentioned drawbacks are not limited to the liquid crystal display device having the constitution shown in FIG. 5, and also occur on a liquid crystal display device which mounts a printed circuit board on a lower side of a display region and, further, to a display device which includes a display panel other than the liquid crystal display panel and mounts a printed circuit board on a lower side of a display region.